Milk Thistle Extract

Milk thistles are thistles of the genus Silybum Adans., flowering plants of the daisy family (Asteraceae). They are native to the Mediterranean regions of Europe, North Africa and the Middle East. The name "milk thistle" derives from two features of the leaves: they are mottled with splashes of white and they contain a milky sap. However, it is the seeds of milk thistle that herbalists have used for 2000 years to treat chronic liver disease and protect the liver against toxins. Increasing research is being undertaken on the physiological effects, therapeutic properties and possible medical uses of milk thistle.

 Description and classification

  Members of this genus grow as annua or biennial plants. The erect stem is tall, branched and furrowed but not spiny. The large, alternate leaves are waxy-lobed, toothed and thorny, as in other genera of thistle. The lower leaves are cauline (attached to the stem without petiole). The upper leaves have a clasping base. They have large, disc-shaped pink-to-purple, rarely white, solitary flower heads at the end of the stem. The flowers consist of tubular florets. The phyllaries under the flowers occur in many rows, with the outer row with spine-tipped lobes and apical spines. The fruit is a black achene with a white pappus.

Only two species are currently classified in this genus:

• Silybum eburneum Coss. & Dur., known as the Silver Milk Thistle, Elephant Thistle, or Ivory Thistle 
  • Silybum eburneum Coss. & Dur. var. hispanicum 
• Silybum marianum Gaertner, the Blessed Milk Thistle, which has a large number of other common names, such as Variegated Thistle. 

The two species hybridise naturally, the hybrid being known as Silybum × gonzaloi Cantó , Sánchez Mata & Rivas Mart. (S. eburneum var. hispanicum x S. marianum)

A number of other plants have been classified in this genus in the past but have since been relocated elsewhere in the light of additional research.

S. marianum is by far the more widely known species. Milk thistle is believed to give some remedy for liver diseases (e.g. viral hepatitis) and the extract, silymarin, is used in medicine. Mild gastrointestinal distress is the most common adverse event reported for milk thistle. The incidence is the same as for placebo. A laxative effect for milk thistle has also been reported infrequently.

  Milk Thistle Nomenclature

Traditional milk thistle extract is made from the seeds, which contain approximately 4-6% silymarin. The extract consists of about 65-80% silymarin (a flavonolignan complex) and 20-35% fatty acids, including linoleic acid. Silymarin is a complex mixture of polyphenolic molecules, including seven closely related flavonolignans (silybin A, silybin B, isosilybin A, isosilybin B, silychristin, isosilychristin, silydianin) and one flavonoid (taxifolin). Silibinin, a semipurified fraction of silymarin, is primarily a mixture of 2 diasteroisomers, silybin A and silybin B, in a roughly 1:1 ratio. In clinical trials silymarin has typically been administered in amounts ranging from 420-480 mg per day in two to three divided doses. However higher doses have been studied, such as 600 mg daily in the treatment of type II diabetes and 600 or 1200 mg daily in patients chronically infected with hepatitis C virus. An optimal dosage for milk thistle preparations has not been established. 

 Health benefits

 Reviews of the literature covering clinical studies of silymarin vary in their conclusions. A review using only studies with both double-blind and placebo protocols concluded that milk thistle and its derivatives "does not seem to significantly influence the course of patients with alcoholic and/or hepatitis B or C liver diseases." A different review of the literature, performed for the U. S. Department of Health and Human Services, found that, while there is strong evidence of legitimate medical benefits, the studies done to date are of such uneven design and quality that no firm conclusions about degrees of effectiveness for specific conditions or appropriate dosage can yet be made.

A review of studies of silymarin and liver disease which are available on the web shows an interesting pattern in that studies which tested low dosages of silymarin concluded that silymarin was ineffective, while studies which used significantly larger doses concluded that silymarin was biologically active and had therapeutic effects.

 Toxin-induced Liver Damage

Research suggests that milk thistle extracts both prevent and repair damage to the liver from toxic chemicals and medications. Workers who had been exposed to vapors from toxic chemicals (toluene and/or xylene) for 5-20 years were given either a standardized milk thistle extract (80% silymarin) or placebo for 30 days. The workers taking the milk thistle extract showed significant improvement in liver function tests (ALT and AST) and platelet counts vs. the placebo group.

The efficacy of silymarin in preventing drug-induced liver damage in patients taking psychotropic drugs long-term has been investigated . This class of drugs is known to cause liver damage from oxidation of lipids. Patients taking silymarin in the study had less hepatic damage from the oxidation of lipids than patients taking the placebo.

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